The modern curtain wall has evolved from static wrapper to active building system.

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By Sara Hart

More than a wrapper

Process has never been more important as sustainability becomes an essential performance criterion and forces the interdependence of the systems in order to meet its objectives. Facades are no longer mere wrappers. They are another vital system that can improve or undermine the whole-building approach. For the Sobanski addition, the client wanted to maximize natural ventilation while providing indoor comfort mechanically during peak summer and winter conditions. This might be called having it both ways, or, as the engineers describe the solution, “a mixed-mode building-environment-control concept.” More crucial to the process approach, the facade solution must be part of a total building concept.

Photos: © Louise Pieterse External glass blades on the Sobanski Palace facade act as sun “blinkers.” The blinkers are sandblasted to protect the occupants from oblique solar glare. The floor-plan depth is shallow; the floor-to-ceiling elevation is high; and the facade is fully glazed—a combination that ensures excellent daylight penetration (left).

The principles of natural ventilation greatly influenced the composition of the fenestration in Warsaw. The fully glazed facade system now incorporates high-performance, thermally reflective, double-glazed units. The operable windows near the ceiling of each floor and at the midpoint are outwardly opening, electrically controlled vents and provide single-sided ventilation. Successful ventilation of this type depends on adequate floor-to-ceiling height and the position and size of the operable windows. By increasing the ceiling height, the natural rising temperature gradient between floor and ceiling is increased and pulls outside air through the openings in the facade. Tanno concedes that this type of strategy probably would not work in a heavily partitioned space, but it works very well at Sobanski, which has an open plan and lightly partitioned spaces.

The facade design allows for nighttime opening of the upper vents, which, when coupled with the thermal mass of the exposed concrete floor slabs, will typically lower space temperatures by a few degrees in summer. “The high-level ones are automatically controlled by the Building Management System (BMS) and only operate at night to cool the structure,” explains Tanno. “The mid-level vents are occupier- controlled and are normally shut when the BMS operates the high-level ones outside office hours. This makes a significant contribution to reducing cooling-plant size and, hence, lowering capital and operating costs.”

Vertical glass blades on the exterior act as sun “blinkers.” The blinkers are sandblasted to increase opacity and protect occupants from oblique solar glare while letting diffused light into the interiors. In order to mitigate the possibility of thermal-shock fractures, the blinkers were made of thermally toughened glass. The idea of screening a facade with cantilevered glass fins was a bold one, and its success, Tanno maintains, is due to a carefully considered collaboration among the Polish contractor, the Italian fabricator, and the engineers. (The facade fabricator/contractor was Aluglass International. The curtain-wall system it adapted specifically for this project was Far-Wall 200 from the Italian company Progetti.) “It helped the contractor enormously to work from a set of clear and concise intent details, developed by our facade engineers,” explains Tanno.

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